(a) Field of the Invention
This invention relates to an endoscope and more particularly to an automatic focus detecting mechanism for endoscopes.
(b) Description of the Prior Art
Generaly, in an observation of the inside of a body by an endoscope, the focusing is effected by adjusting the position of an objective lens system by rotating a focus adjusting ring arranged outside of the body. In this case, it is desirable to effect the focusing rapidly from the necessity to end the observation and photographing as fast as possible in consideration of the pain of a patient when an endoscope optical system is inserted inside of his body. However, because of the necessity of frequent focusing in spite of a large depth of focus of the objective lens owing to the uneveness of the surface of the object to be observed and accordingly owing to the frequent changing of the observing position, the time and the work needed for focusing are very troublesome for the patient as well as for the operator. Therefore, it has been proposed to provide an endoscope having an automatic focus detecting mechanism. However, in conventonal endoscopes, a light receiving device of a focus detecting mechanism is arranged on the objective lens side in respect of an image guide (an optical fiber bundle for image transmission). Therefore, there is a merit enabling a stereoscopic vision, double image coinciding method or the like, but, on the other hand, there is a problem that the endoscope would be bulky and complicated manufacture.